1. Field of Invention
Although it may be used for other purposes, this invention relates primarily to bubbler devices for transferring electronic grade organometallic compounds from a container having such compounds therein to a deposition system, for example, a chamber wherein crystalline or other substances are being grown on substrates or are otherwise being treated by a process known as "doping" in production of products such as semiconductor elements or monolithic circuits.
2. Description of Prior Art
It is known in the prior art to use a bubbler technique for transferring, by vapor deposition, doping compounds in liquid form from a source of such compounds, e.g., a non-refillable cylindrical cartridge, to a deposition system. Such bubbler technique involves the introduction, through an inlet valve and a dip tube, to the bottom of the cylinder, of a gas (such as hydrogen) which is inert to the doping compound. In bubbling up through the doping compound, molecules of the compound intermingle with those of the gas. The gas, saturated with the vapor of the compound, flows out through the outlet valve where it enters the deposition system. It has generally been the practice in the prior art to use bellows seal valves for both the inlet and outlet valves.
Bubbler cylindrical cartridge and dip tube assemblies including inlet and outlet valves, as mentioned above, are commercially available, a typical example being the assembly manufactured and sold by Thiokol/Ventron Division Alfa Products, 152 Andover Street, Danvers, Mass. 01923. These prior art cylindrical cartridge and dip tube assemblies are characterized in that they are intended to protect the organometallic compounds during shipment and storage as well as to provide a method for dispensing the compound to a deposition system.
A number of problems with such bubbler assemblies or devices have been encountered in the prior art. Not only are the organometallic compounds easily contaminated, but they are also prone to leakage. This situation has been aggravated in the prior art by the shape and arrangement of the cylindrical cartridge or cylinder, the bottom portion having a generally oval shape narrowing down to size of an opening that is provided for filling the cartridge and which is closed by a threaded plug. Such cylinders thus have the disadvantage of not being stable in an upright position and also of having a tendency to leak in the upright as well as other positions. The narrowing or oval shape of the lower portion of the prior art cartridges has a further disadvantage in that it detracts from an overall average consistency or uniformity in the rate of transfer of the organometallic vapour from the cartridge to the deposition system. The reason for this is that the volume of the liquid through which the continuing flow of the bubbles rise to become saturated with the organometallic vapor diminishes as the level of the liquid drops.
Since the organometallic compounds are very costly, such contamination, leakage, and the inability to utilize uniformly the complete contents of the cartridge added significantly to the cost and reduced the efficiency of the doping procedures.
One attempt to overcome the disadvantages of the prior art devices hereinabove described is disclosed in U.S. Pat. No. 4,506,815, issued Mar. 26, 1985 (Melas et al.), wherein an all welded cylinder and dip tube package utilizing diaphragm valves at each of the inlet and outlet valves and having the interior of the cylinder and the interior and exterior of the dip tube provided with a coating of a material which acts as a barrier to the contamination of the organometallic liquid by the metal is described. Specifically, the device described in said patent comprises pipe connections between the inlet and outlet openings of the top closure portion of the device and the diaphragm valves which control passage of gas into the cylinder and passage of the gas saturated with the organometallic compound vapors out of the cylinder, respectively, the pipe connections being sealed by welding. Although the device disclosed in the said patent represented an improvement over prior art devices in the bubbler device art, problems are associated with it as well. In particular, since the valves extend outwardly from the top closure portion of the device in a wing-like manner, there exists the potential for cracking of the pipe welds during handling, for example, presenting the possibility of leakage.